Henry David Thoreau rhapsodized shamelessly about White and Walden ponds, calling them "Lakes of Light" and "great crystals on the surface of the earth." Living on a pond became, for the 19th-century writer, something of a vocation. So, too, for a modern couple, whose 140 hilly acres in California's Napa Valley contained numerous potential sites, all of them glorious. Even so, from their point of view, there was only one spot—a waterside one—on which to build. The owner consulted with more than a few architects; Howard J. Backen, of Backen Gillam Architects, who got the commission, brought the house close to this diminutive body of water and made a point of respecting its scale. "The pond set the parameters," he says.

"The scheme really had to be mindful of the serenity of that delicate, bowl-shaped pond. Anything but a small residence would have been a mistake." Approached from the land, the 2,960-square-foot structure can scarcely be discerned. "The idea of the house was to make it go away as much as possible," explains Backen (whose firm has offices in the Northern California towns of St. Helena and Sausalito). "People drive right by it," its owner adds, grinning. Seeded with the same grasses and indigenous plants as the surrounding chaparral—"that Steinbeckian California landscape," as his girlfriend describes it—the sod roof acts as camouflage, changing with the seasons, becoming verdant in the winter rains, tawny in summer heat.

Overnight visitors bed down on a guest boat. From its deck, the house, with its watery reflection, casts a distinctly cinematic spell.

The residents admire the restraint of Japanese houses. Their own feels similarly understated, unfolding in a series of simple rectilinear planes. The effect is disciplined, serene and diametrically opposed to some other places in the wine country, where, in the past few years, outsize mansions seem to have sprouted up in clusters, like mushrooms after a rain. From the water the house looks anything but earthbound; its three terraces appear to float. To create this effect, Backen drained the pond, setting the foundation back 18 inches from shore, then cantilevered the terraces out six feet into the water. "It was a feat of construction," he allows.

Those who can actually find the residence enter at roof level, making their way down an exterior stone staircase to the main entrance—a pair of sliding wood-and-agate shoji screens. Once inside, they're brought face to face with the view. "Everything opens out to the pond," Backen says. The house, which is set at an angle that parallels the shoreline, consists of three parts: a kitchen/dining/living room; a master bedroom, bath and library; and an office and garage. The architect was building his own house, just five miles away, at the same time he designed the pondside one, and decisions were sometimes made during his client's impromptu visits to that site. "I'd go to his place and say, Damn, that living room is too long; I don't want it this long,'" the client recalls. In this way they arrived at the right length for the couple's own main room—just under 45 feet. They kept its scale manageable by limiting the ceiling height (to nine feet, six inches). "If you have a 10- or 12-foot ceiling, you have a big, important room— it's not welcoming," the owner explains.

The bi-parting floor-to-ceiling doors, which were designed by Backen, provide endless versatility. "When the doors are open, it's an open-air pavilion; when the screens are pulled, it's a screen porch," the architect says. Thanks to this cross ventilation, as well as the sod roof's insulating properties, no air-conditioning is necessary. An architecture maven, the owner contributed numerous ideas, including the living room's distinctive crisscrossed ceiling. "We first had a hemlock ceiling, then saw this ceiling in a picture of a Japanese house," he remembers. The two-by-12-foot hemlock strips that traverse the room bring "just the right amount of lightness to the plaster. It gives an airy feeling."

The architect set the house's tone— quite literally—by suggesting that the cut stone used around the base of the building, both inside and out, be of a light hue. "We came up with a color suitable for the exterior and interior based on that stone," says interior designer Jacques Saint Dizier, who practices in the Sonoma County town of Healdsburg (with a satellite office in Hawaii). The inside walls are a wheat shade; the outside ones are a deeper still, a kind of sepia.

In the main room, Saint Dizier worked in a palette that reflects the landscape; the sea-grass carpet is just one element that "pulls that pale golden color from the hillside in," he says. This is an unfussy, almost masculine interior. In this clutter-free zone, substantial pieces square off against equally forceful ones, including expansive buffalo-leather sofas and lounge chairs upholstered in forest-green mohair. Almost every piece has a strong silhouette, with personality to spare.

The house is deliberately small—just one bedroom. "You have to adjust you way of thinking about possessions if you live here," the client's girlfriend says Adjust, as in divest. Any new acquisitions tend to be Asian-inspired, including the handsomely crafted cabinets of mahogany, maple and Japanese paper, in which the couple store their clothes "We wanted to stay with the Pacific Rim influence that runs throughout the interior," says Saint Dizier.

The library is the locus of some high stakes card playing and the only room that doesn't overlook the water. "He didn't want the group to be distracted, Backen teases. Its simple, geometric mahogany shelving unit, by Saint Dizier "creates spaces so they can showcase their collection of Asian art, which is quite extensive and quite beautiful," the designer says. Overnight visitors bed down on the water—or, more precisely on the couple's newly acquired 26-foot yellow-hulled guest boat. From its deck the house, with its watery reflection casts a distinctly cinematic spell; each window seems to frame a scene.

The greatest pond lover of them all— Thoreau—once wrote that Walden was "a mirror which no stone can crack whose quicksilver will never wear off whose gilding Nature continually repairs." This couple speak in similarly awestruck tones. "I'd never lived on water before," says the owner. "I didn't know all the wonderful things that would come with it, the reflection and the light."

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